Analysis and simulation of dry-spot behavior in Liquid Composite Molding

Abstract

Due to industrial automation of liquid composite molding processes and increasing geometrical complexity of composite components, dry-spots from flow front junctions have become increasingly difficult to avoid. The impact and behavior of voids (microscopic gas entrapments) during preform impregnation in Liquid Composite Molding processes is well known but little attention is given to behavior of dry-spots (macroscopic gas entrapments). Experiments show, that formation of dry-spots in an early stage of an injection process does not necessarily lead to scrap parts. Therefore simulation based predictions of dry-spots are not a sufficient condition for bad injection strategies. Resolution mechanisms of dry-spots under controlled process conditions and the resulting findings of fundamental formation- and dispersion mechanisms are briefly presented. Parameters that have an influence on the diminishing rate of dry-spots have been identified and correspond to Darcys law. Consequently this paper presents a first approach of dry-spot size prediction, which shows good agreement with experimental results. The two-phase simulation is based on the pressure-saturation approach formulated using Darcy´s law. A relative permeability model takes into account the influence on the flow of each phase in the presence of the other phase.